Monarch, CO, was the site of a large quarry located at the western end of the D&RG(W)'s Monarch Branch at the eastern foot of Monarch Pass. It was located to the west of the old town of Garfield, CO?.

The site began as the location of the Madonna Mine?, one of the silver mines established following Nicolas Creede's 1879 discovery of silver on Limestone Mountain (today's Monarch Mountain). The railroad was extended from Maysville west to Monarch in 1883 on account of a silver mining boom. This only lasted about 10 years, until the Silver Panic of 1893? made mining uneconomical.

In addition to the precious metal ores in the area, Colorado Fuel & Iron determined rock surrounding the mine was a high quality source of dolomite and limestone that could be used in its Pueblo blast furnaces. Quarrying of flux rock sustained the branch until the shutdown of CF&I's blast furnaces in Pueblo in 1982. At that point, limestone from Monarch was no longer needed and the rails were abandoned in 1984. Low level quarrying continues today, but rock is hauled out by truck.